Device for heating compressed air, particularly for heat bonding purposes in folding box machines



ug.. l5, w67 W. H. HITTENBERGER ET AL 3,336,464

DEVICE FOR HEATING COMPRESSED AIR, PAHTICUL ARMY VOR HEAT BONDING PURPOSES IN FOLDING BOX MACHINES Filed Feb. 25, 1965 3 Sheets-Sheet l INVENTOR. Wfl/fam /v H/'fenberger Henry J. D60 50H15 6'. Pose/7 www mh ,4 TTU/mfr ug- 35, i967 W. H. HITTENBERGER ET AL 3,336,464

DEVICE FOR HEATING COMPRESSED AIR, PARTICULAHJY FOR' HEAT BONDING PURPOSES IN FOLDING BOX MACHINES Filed Feb. 25, 1965 s sheets-sheet S/L /CON CARB/0E i INVENTOR. W/Y//am /vf'enberger /venry J. Dea Bor/.s S. Posen ugi5, w67 vv. H. HITTENBERGER ET AL 3,335,464

DEVICE FOR HEATING COMPRESSED AIR, ARTICULAHLY FOR HEAT BONDING PURPOSES IN FOLDING BOX MACHINES Filed Feb. 25, 1965 3 Sheets-Shaw Z3 INVENTOR W/Y//am //energer Henry J. Dea Bor/s JI Pose/7 #www 'uw ATTORNEY United States Patent C Henry l. Dea, @ak- Los Altos, Calif., assignors New York, NY., a corporation ABSTRACT F Til-IE DISCLUURE The present improvements provide an electric heater of the concentric multi-chamber type for heating compressed air to temperatures of the order of 1000 degrees F. Two spaced concentrically disposed tubes are joined intermediate their ends and are provided with flanges at their ends to which centrally apertured stacks of closure discs are secured. One of the stacks comprises an inner disc resting on the ange and provided with an aperture within which the inner tube is seated and an outer disc having a smaller aperture in which a sealing plug of a carbonaceous heater element is fitted. The heater is tiltable and its discharge nozzle is tangentially disposed with respect to a circle about the tilt axis, thus permitting the nozzle to be withdrawn from a narrow space between folding box panels about to be heat sealed.

In folding box machines in which certain panels or flaps of a folding box are to be bonded to other panels or flaps by means of a preapplied thermoplastic adhesive, heating means are required to convert the adsesive from its normal state of non-tackiness into a tacky state.

The adhesive may be preapplied either in certain predetermined areas to the panels or aps to be bonded, or the entire box blank may have a coating of a thermoplastic material on one or both sides, primarily applied for the purpose of rendering the paperboard resistant to moisture-vapor or even liquid.

Such coatings are extremely thin, yet it is possible by proper handling to bond two such adhesive coated box portions together and thus secure box corner portions together or seal the lled box. The copending application of Hittenberger et al. Ser. No. 435,281, led Feb. 25, 1965 discloses and claims a method of securely bonding such thin thermoplastic coating at extremely high production rates.

The disclosed method calls for application of highly concentrated heat to the coated board without mechanical contact of a heating element with the coating and for application for an extremely brief period of time of the order of one-tenth of a second in order to soften the coating effectively by mere surface heating yet without transfer of any appreciable amount of heat by conductance through the board itself.

This is accomplished by applying a blast of hot air to the coating at a temperature Well above the char point of the board, representative discharge temperatures of the air being of the order of 900 F. (480 C.).

This poses problems in that a high energy input is required, yet it is undesirable to heat the machine or the air about the machine to a material extent by the presence of the heater or heaters. In a folding box forming machine it is undesirable to operate an unduly hot machine, as the temperature influences the physical characteristics of the blanks to be set up. In a box closing machine, particularly one for sealing frozen food boxes, it is undesirable to subject the filled boxes to heat, except for brief periods.

3,336,464 Patented Aug. l5, 1957 Furthermore it is essential that the warm-up time of the machine be short. Wire-wound or ribbon-Wound electric resistance elements are for this reason not favored, as a long time elapses until the core on which the elements are wound assumes its proper operating temperature.

Also the heat generating surface area of such wound heating elements is only a fraction of the total surface area and wound elements are sensitive to electric overloads or, conversely, are limited in heat output per unit of surface area.

A further requirement for an effective air heating and heated-air applying device is that zones of expansion of the heater air be avoided, as any expansion of air is ac companied by a corresponding drop in temperature.

The present invention provides a heater of high efticiency and low radiation loss.

- This is accomplished by-among other structural details-a concentric two-chamber arrangement traversed by the compressed air, rst in a helical path providing a flow path of very substantial length in relation to the physical dimensions of the device, and then in a turbulent path along a rod type electric heating element. The air then passes into an appropriately shaped discharge nozzle which is maintained at a very close distance to the coated board surface.

By tests it was determined that commercially available carbonaceous resistance heating rods originally developed and produced for the heating of furnaces and kilns are admirably suited for the present air heater.

For example, units rated at 2,800 watts and being of an effective length of 12 inches (30 cm.) to which there is added a low resistance portion of 3 inches (7.5 cm.) at either end, the total resistance varying between 0.83 ohm and 1.0 ohm can be operated at a load of 4,550 Watts in the air heater of this invention as a result of Which air discharge temperatures between 900 and 1400 degrees F. (480-760 C.) are readily obtainable of air discharged at the rate of about 2.6 cu. ft./min. (74 l./min.).

Such a range is amply suliicient for the flash heating of thermoplastic coatings for very brief durations, such as between 6 and 13 hundredths of a second.

While we are aware that it is known to soften and render tacky thermoplastic lms by the application of jets of heated air, we are not aware of known devices capable of furnishing a continuous flow of highly heated air, as the device hereinafter described, without heating the surroundings appreciably. It should be remembered in this connection that a machine for sealing three aps of a cover requires three air heaters at spaced locations of the machine.

The objects, features and advantages of this invention will appear more fully from the detailed description which follows accompanied by drawings showing, for the purpose of illustration, a preferred embodiment of the invention. The invention also resides in certain new and original features of construction and combination of elements hereinafter set forth and claimed.

Although the characteristic features of this invention which are believed to be novel will be particularly pointed out in the claims appended hereto, the invention itself, its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part of it in which:

FIG. 1 is a perspective view of an air heater embodying the present invention;

FIG. 2 is a perspective view of the air heater of FIG. l partially disassembled; and

FIG. 3 is a longitudinal section of the device illustrating the air passage therethrough.

In the following description and in the claims various details will be identified by specific names for convenience. The names, however, are intended -to be generic in their application. Corresponding reference characters refer to corresponding parts in the several figures of the drawings.

The drawings accompanying, and forming part of, this specification disclose certain specific details of construction for the purpose of explanation of broader aspects of the invention, but it should be understood that structural details may be modified in various respects without departure from the principles of the invention and that the invention may be incorporated in other structural forms than shown.

Referring to FIG. 1 the air heating device comprises a tubular housing 11 to which a mounting device 12 is secured. The mounting device is shown in FIG. l only and comprises a pivot block 13 and a counter block 14. Both blocks form a clamp within which the housing 11 is held by two clamp bolts of which one is visible at 15. A pivot shaft 16 extends through the pivot block 13 and permits pivotal mounting of the entire device in the box machine, for example a folding box sealing machine, for which the heating device is designed.

The counter block is further secured to the housing by a U bolt 17. In actual use in a folding box machine the movable element of a suitable servo-motor is attached to the counter block in order to rock the heating device about its shaft axis 16 from an operative into an inoperative position and back again.

An air inlet duct 18 is secured to the housing substantially tangentially in order to `convey air into the interior of the housing in a tangential direction to cause the air to pass through the housing along a helical path.

Referring now to FIG. 3 showing the interior of the housing 11, it is seen that the housing is construction of two substantially concentric shells 19, and three anges 21, 22, 23. In addition there is a discharge nipple Z4 having a flange 25.

The outer shell 19 has a larger diameter and a shorter length than the inner shell 20 which, for this reason, protrudes therefrom beyond the intermediate flange 22. The shells define an outer chamber 26 into which the duct 13 leads and an inner chamber 27 from which the flanged nipple 24 leads.

The outer chamber 26 which communicates with the inner chamber 27 at the right end at which slots 28 are formed in the inner shell. There are four such slots, as is also apparent from FIG. 2. These slots break up the ow of air leaving the outer chamber and cause the air to pass through the inner chamber in a turbulent state.

The outer ends of the chambers 26 and 27 are closed by asbestos plates or discs 29 at the right and plates or discs 30 at the left (FIG. 3). It should be noted that FIG. 1 shows the heating device reversed with respect to FIGS. 2 and 3. Hence right and left are reversed in FIG. l.

A resistance heating element or rod 31 extends centrally through the inner chamber 27 and protrudes through central holes in the discs 29 and 30. Asbestos stuffing 43 in the central holes seals the inner chamber against the outside.

The rod 31 shown in FIG. 2 is a silicon carbide rod having a central high resistance portion 32 which is 12 inches ('30 cm.) in length and has low resistance ends, each end being 3 inches (7.5 cm.) in length welded or sintered thereto. This arrangement makes the central portion the principal heat generating portion, whereas the end portions serve as terminals for the connection of leads thereto. FIG 2 shows substantially U shaped sheet metal clips 34 and braided terminal straps for this purpose.

FIG. 1 shows that in the assembled unit the ends of the rod are protected against damage by cover discs 36 on spacer studs 37.

A discharge nozzle head 33 of angular design is secured to the discharge flange 25. The head 38 comprises two curved walls 39 and 40 provided with nozzle apertures l 41. The curvature of the two Walls 39 and 40 resembles that of an airfoil.

The chamber formed by the walls 39 and 4) is closed at the end by a spacer fin protruding about 1/16 of an inch (1.6 mm.) beyond the surface of the walls. The purpose of the spacer fin 42 is to space paperboard panels urged towards the walls 39, 46 by an accurately gaged distance of j/16 inch (1.6 mm.) from the apertured walls 39 and 40.

Turning now to the operation of the device, the straps 35 are connected to a suitable source of electric power, preferably a transformer having a plurality of taps in its secondary winding to permit variation of the voltage. The voltage applied to the illustrated device was variable from 65 v. upwards in increments of 2.5 v.

Prior to connection to electric power, air is supplied to the duct 18 from a suitable source of compressed air. The illustrated air heater was supplied from a four-stage air turbine passing 2.6 cu. ft. l.) per minute through the chambers.

At a particular voltage setting the temperature of the discharged air was measured by a thermocouple inserted into one of the holes and found to be 900 degrees F. (480 C.). Only s of an inch away from the discharge hole the air temperature was found to be 180 degrees F. (82 C.) lower, a result of cooling-by-expansion.

In order to avoid cooling-by-expansion phenomena within the air passages the annular cross sectional area of the outer chamber 26 is made equal to the annular cross sectional area of the inner chamber 27 and the slots 23 are dimensioned to equal the cross sectional area of the chambers, so that no air expansion occurs within any portion of the air passage.

Similarly, the nozzle head 38 is designed to provide a passage which slightly decreases in cross sectional area towards the apertures 41.

The angular shape of the head 33 is so designed that its walls 39, 4u lie substantially tangentially with respect to a circle about the tilt shaft 16. Thus, by tilting the unit about the shaft 16, the nozzle head 33 may be withdrawn along an arcuate path from an active position, for example the position in which the head is straddled by a box body wall and a box cover ap forming an inverted V into which the head extends when heating the wall and flap.

What is claimed is:

1. A device for electrically heating compressed air, the

device comprising a pair of substantially concentrically disposed spaced metal tubes, one inside the other, forming an outer air chamber between them, one end of the outer tube being closed and secured to the inner tube, a portion of which projects beyond the said one end of the outer tube, an outlet passage being provided in the projecting portion, said outlet passage having a discharge nozzle connected thereto, there being an air inlet passage in the wall of the outer tube adjacent said one end and a transfer passage in the wall of the inner tube adjacent the other end of the outer tube for passage of air from said outer air chamber to the interior of the inner tube, said other end having a terminal flange connected thereto, said inner tube extending beyond said terminal flange, an assembly of stacked discs on said terminal flange, the disc immediately adjacent the flange having an aperture therethrough in which said inner tube is seated, the outermost disc having a smaller aperture therethrough; a sealing plug in said assembly; centrally apertured means for closing the projecting portion of the inner tube; a sealing plug in said apertured means; and a heater element in the form of a carbonaceous rod extending through the sealing plugs at both ends of the chamber formed by the inner tube. Y 2. A device according to claim 1 in which the projecting portion of the inner tube is fitted with a ange and in which the apertured closing means comprises a stack of centrally apertured discs.

3. An air heating device according to claim 2 in which 5 the air inlet passage is tangentially disposed with respect to the outer chamber to feed air into said outer chamber in a substantially tangential direction with respect thereto so as to cause air to traverse the outer chamber along a helical path to said other end thereof.

4. An a'ir heating device according to claim 2 in which the cross sectional annular area of the outer chamber, the cross sectional annular area of the inner chamber and the total area of the said transfer passage are substantially equal.

5. An air heating device according to claim 2 in which means are provided for tilting the device about a tilt axis transverse to the axis of the outer tube and in which the discharge nozzle is provided with opposite perforate Walls 6 stantially tangentially disposed with respect to a circle about said tilt axis.

References Cited UNITED STATES PATENTS 2,609,477 9/1952 Borda et al 219-380 2,797,297 6/ 1957 Nihlen 219-381 X 2,837,623 6/1958 Judson et al 219-374 X 2,868,944 1/ 1959 Koch et al 219-379 X 3,249,024 5/ 1966 Shiu 219-374 X FOREIGN PATENTS 985,944 3/1951 France. 936,648 9/ 1963 Great Britain.

through which the air is discharged, the walls being subl5 ANTHONY BARTIS, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0F lCORRECTION Patent No 3 ,336 ,464 August 15 1967 William H. Httenberger et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

a Column 4, line 75, and column 5, lines 6 and 1l, for the claim reference numeral "2", each occurrence, read 1 Signed and sealed this 6th day of August 1968.

(SEAL) Attest:

EDWARD J. BRENNER E dward M. Fletcher, Ir.

Commissioner of Patents Attesting Officer 

1. DEVICE FOR ELECTRICALLY HEATING COMPRESSED AIR, THE DEVICE COMPRISING A PAIR OF SUBSTANTIALLY CONCENTRICALLY DISPOSED SPACED METAL TUBES, ON INSIDE THE OTHER, FORMING AN OUTER AIR CHAMBER BETWEEN THEM, ONE END OF THE OUTER TUBE BEING CLOSED AND SECURED TO THE INNER TUBE, A PORTION OF WHICH PROJECTS BEYOND THE SAID ONE END OF THE OUTER TUBE, AND OUTLET PASSAGE BEING PROVIDED IN THE PROJECTING PORTION, SAID OUTER PASSAGE HAVING A DISCHARGE NOZZLE CONNECTED THERETO, THERE BEING AN AIR INLET PASSAGE IN THE WALL OF THE OUTER TUBE ADJACENT SAID ONE END AND A TRANSFER PASSAGE IN THE WALL OF THE INNER TUBE ADJACENT THE OTHER END OF THE OUTER TUBE FOR PASSAGE OF AIR FROM SAID OUTER AIR CHAMBER TO THE INTERIOR OF THE INNER TUBE, SAID OUTER END HAVING A TERMINAL FLANGE CONNECTED THERETO, SAID INNER TUBE EXTENDING BEYOND SAID TERMINAL FLANGE, AN ASSEMBLY OF STACKED DISCS ON SAID TERMINAL FLANGE, THE DISC IMMEDIATELY ADJACENT THE FLANGE HAVING AN APERTURE THERETHROUGH IN WHICH SAID INNER TUBE IS SEATED, THE OUTERMOST DISC HAVING A SMALLER APERTURE THERETHROUGH; A SEALING PLUG IN SAID ASSEMBLY; CENTRALLY APERTURED MEANS FOR CLOSING THE PROJECTING PORTION OF THE INNER TUBE; A SEALING PLUG IN SAID APERTURED MEANS; AND A HEATER ELEMENT IN THE FORM OF A CARBONACEOUS ROD EXTENDING THROUGH THE SEALING PLUGS AT BOTH ENDS OF THE CHAMBER FORMED BY THE INNER TUBE. 